Cortical Reaction in Sea Urchin | Slow Blocks to Polyspermy

Summary

This video delves into the slow block mechanisms of polyspermy in sea urchins, focusing on cortical granulation. It explains how the first sperm triggers the release of soluble factors that activate tyrosine kinase, leading to the production of IP3 and DAG. These components initiate a cascade that raises intracellular calcium levels, prompting the exocytosis of cortical granules. The granules release proteins and enzymes that harden the fertilization envelope, preventing additional sperm entry. The video also touches on the role of ovoperoxidase in cross-linking proteins and forming a robust barrier, ensuring fertilization by a single sperm.

Takeaways

• 🔬 The video discusses the process of fertilization in sea urchins, focusing on the mechanisms that prevent polyspermy.
• 🌊 The first line of defense against polyspermy is the fast block, which is an electrical block triggered by the sperm's entry.
• 🏰 The slow block to polyspermy involves the cortical granules, which are located inside the egg cell.
• 🚀 Upon successful sperm entry, the sperm releases soluble factors that activate tyrosine kinase, initiating the slow block mechanism.
• 🔄 Tyrosine kinase activates phospholipase C (PLC), which cleaves PIP2 into DAG and IP3, leading to an increase in intracellular calcium levels.
• 🌐 The rise in calcium levels triggers the exocytosis of cortical granules, releasing proteins and enzymes that contribute to the formation of the fertilization envelope.
• 🛡️ Cortical granule substances (CGSP) and transglutaminase (TG) cross-link proteins in the fertilization envelope, hardening it to prevent further sperm entry.
• 🌀 Hydrogen peroxide is produced by the egg, which, along with TG and ovoperoxidase (OVO-POD), cross-links proteins to strengthen the fertilization envelope.
• 🔗 The presence of H2O2 generated by an egg oxidase/OVO-POD catalyzes the formation of covalent tyrosine bonds, further solidifying the fertilization envelope.
• 👍 The video encourages viewers to like, subscribe, and support the channel's work on Patreon.

Q & A

What is the main topic of the video?

The main topic of the video is the process of fertilization in sea urchins, specifically focusing on the slow blocks to polyspermy.

What are the fast blocks to polyspermy mentioned in the video?

The fast blocks to polyspermy, also known as electrical blocks, are the initial barriers that prevent multiple sperm from entering the egg.

What is the role of the cortical granules in the fertilization process?

Cortical granules play a crucial role in the slow block to polyspermy by releasing proteins and enzymes that help create the fertilization envelope, which hardens to prevent additional sperm from entering.

How does the sperm activate the tyrosine kinase during fertilization?

The sperm releases soluble factors that activate the tyrosine kinase, which is part of the mechanism leading to the slow block to polyspermy.

What is the function of PLC in the fertilization process?

Phospholipase C (PLC) is activated by tyrosine kinase and cleaves the membrane-bound PIP2 into DAG and IP3, which are essential for the release of calcium ions from the endoplasmic reticulum.

How does the release of calcium ions into the cytoplasm contribute to the fertilization process?

The release of calcium ions into the cytoplasm leads to an increase in intracellular calcium levels, which triggers the exocytosis of cortical granules, aiding in the formation of the fertilization envelope.

What is the role of CGSP in the formation of the fertilization envelope?

CGSP, an enzyme released by the cortical granules, cleaves the proteins linking the fertilization envelope to the cell membrane, contributing to the hardening of the fertilization envelope.

What is the significance of hydrogen peroxide in the fertilization process?

Hydrogen peroxide is produced by the sea urchin egg and is involved in the cross-linking of proteins in the fertilization envelope, making it more impermeable to additional sperm.

How does the presence of H2O2 generated by an egg oxidase contribute to the fertilization process?

The H2O2 generated by an egg oxidase interacts with peroxidase to catalyze the formation of covalent tyrosine bonds between proteins, further hardening the fertilization envelope.

What is the purpose of the fertilization envelope in the context of the slow block to polyspermy?

The fertilization envelope serves as a physical barrier that prevents additional sperm from entering the egg after the first successful sperm, thus ensuring that only one sperm fertilizes the egg.

How does the video encourage viewers to support the content creator?

The video encourages viewers to give a thumbs up, subscribe to the channel, and consider supporting the creator's work on Patreon.

Outlines

00:00

🐙 Sea Urchin Fertilization and Polyspermy Block

This video discusses the process of fertilization in sea urchins, focusing on the mechanisms that prevent polyspermy, the condition where more than one sperm fertilizes an egg. The video explains the role of cortical granules in creating a fertilization envelope that blocks additional sperms. It details the activation of tyrosine kinase by sperm-released factors, which leads to the production of IP3 and DAG, causing the release of calcium ions from the endoplasmic reticulum. This increase in calcium triggers the exocytosis of cortical granules, releasing proteins and enzymes that harden the fertilization envelope. The video also mentions the role of ovoperoxidase in cross-linking proteins and the formation of a highly impermeable barrier to ensure monospermy.

Keywords

💡Fertilization

Fertilization is the process by which an egg is penetrated by a sperm to form a zygote, marking the beginning of development in sexually reproducing organisms. In the context of the video, fertilization in sea urchins is the main theme, with a focus on the mechanisms that prevent multiple sperm from fertilizing the same egg.

💡Polyspermy

Polyspermy refers to the condition where more than one sperm fertilizes an egg, which is generally undesirable as it can lead to abnormal development. The video discusses how sea urchins have evolved mechanisms to prevent polyspermy, ensuring that only one sperm fertilizes the egg.

💡Cortical Granulation

Cortical granulation is a process in which granules within the egg's cortex release their contents into the space between the egg cell membrane and the fertilization envelope. This reaction is part of the slow block to polyspermy, as it helps to create a barrier that prevents additional sperm from entering the egg.

💡Fertilization Envelope

The fertilization envelope is a protective layer that forms around the egg after fertilization, preventing further sperm entry. In the video, it is mentioned that the slow block to polyspermy involves the hardening of this envelope through the action of various proteins and enzymes released by cortical granules.

💡Tyrosine Kinase

Tyrosine kinase is an enzyme that plays a crucial role in signal transduction pathways. In the video, it is activated by soluble factors released from the sperm, which then triggers a series of events leading to the activation of phospholipase C (PLC) and the subsequent block to polyspermy.

💡Phospholipase C (PLC)

Phospholipase C is an enzyme that cleaves membrane phospholipids. In the video, it is activated by tyrosine kinase and goes on to cleave phosphatidylinositol 4,5-bisphosphate (PIP2) into diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3), which are part of the signaling cascade leading to the block to polyspermy.

💡Diacylglycerol (DAG)

Diacylglycerol is a lipid second messenger that remains attached to the membrane and plays a role in activating protein kinase C, which is part of the signaling pathway leading to the block to polyspermy. It is mentioned in the video as a component produced by the action of PLC.

💡Inositol 1,4,5-Trisphosphate (IP3)

Inositol 1,4,5-trisphosphate is a second messenger that triggers the release of calcium ions from the endoplasmic reticulum to the cytoplasm. In the video, it is described as a molecule that, when released, initiates the increase in intracellular calcium levels necessary for the exocytosis of cortical granules.

💡Exocytosis

Exocytosis is the process by which cells expel substances from within the cell by fusing vesicles with the cell membrane. In the video, exocytosis of cortical granules is a key step in the slow block to polyspermy, as it releases proteins and enzymes that help to harden the fertilization envelope.

💡Hydrogen Peroxide

Hydrogen peroxide is a reactive oxygen species produced by the sea urchin egg. In the video, it is mentioned as a product of the reaction catalyzed by ovoperoxidase, which contributes to the cross-linking of proteins in the fertilization envelope, thus strengthening the block to polyspermy.

💡Ovoperoxidase

Ovoperoxidase is an enzyme found in sea urchin eggs that catalyzes the conversion of molecular oxygen into hydrogen peroxide. In the video, it is described as playing a role in the hardening of the fertilization envelope by interacting with other proteins and contributing to the block to polyspermy.

Highlights

Discussion on the fertilization process in sea urchins and the prevention of polyspermy.

Introduction to the slow blocks to polyspermy, including cortical granulation.

Explanation of the formation of a barrier in the zona pellucida of the egg membrane.

Description of the egg's structure with jelly, cortical granules, egg cell membrane, and vitelline membrane.

Mechanism by which the first sperm penetrates the barriers and triggers the first block to polyspermy.

Transition from fast blocks to slow blocks in the polyspermy prevention mechanism.

Release of soluble factors by the sperm that activate tyrosine kinase.

Activation of PLC by tyrosine kinase leading to the cleavage of PIP2 into DAG and IP3.

Release of calcium ions from the endoplasmic reticulum to the cytoplasm.

Role of increased intracellular calcium levels in the exocytosis of cortical granules.

Release of proteins and enzymes from cortical granules that contribute to the fertilization envelope.

Function of CGSP, an enzyme that cleaves proteins linking the vitelline envelope to the cell membrane.

Production of hydrogen peroxide by the sea urchin egg and its role in forming the fertilization envelope.

Cross-linking of proteins in the fertilization envelope by TG + OOP.

Interaction of ovoperoxidase with proteus a, hardening the fertilization envelope.

Formation of covalent tyrosine bonds by egg oxidase/peroxidase, further strengthening the fertilization envelope.

Final explanation of how the slow blocks to polyspermy prevent additional sperm from entering the egg.

Call to action for viewers to like, support, and subscribe to the channel.

Transcripts

Oh in the series of videos we have been

discussing about the fertilization

process in sea urchins all the previous

videos links are in the description now

in this video we'll be discussing about

the slow blocks to polyspermy which

includes the cortical granulation in

this reaction the barrier is made in the

poem of fertilization envelope on the

egg membrane which leads to blocking off

additional spoons here in this diagram

we can see the egg has got jelly on the

outside there are cortical granules

inside the cell it has got egg cell

membrane on the inside and we see it has

got whittling membrane on the outside

when the first successful sperm gets

through these barriers by launching the

I cross numeration as shown in the

diagram then within no time the first

block to polyspermy comes into play

which we have already discussed in the

previous video that is the first blocks

to polyspermy but electrical blocks to

polyspermy or we can say fast blocks to

polyspermy

gradually ventures and then comes the

slow blocks to Polly spool

there is the permanent solution to block

polyspermy in the mechanism of slow

blocks to polyspermy we see the sperm

releases many soluble factors and these

factors are able to activate the

tyrosine kinase if we see it

diagrammatically the sapone releases

factors we turn on the tyrosine kinase

the activated tyrosine kinase further

activates the plc this plc in turn

Cleaves the membrane bound pip2 into two

components da g and i p3 that da g

diacylglycerol remains attached to the

membrane while as i p3 installed trace

phosphate disassociates and gets to

there and applause ming reticulum while

it happens to open the calcium ion

channels with which the calcium ions are

pumped out of endoplasmic reticulum to

the cytoplasm the release of calcium

into the cytoplasm leads to the increase

in the intracellular calcium levels

which aids in the exocytosis of cortical

granules so upon exocytosis these

cortical granules releases many types of

proteins and enzymes which helps in

making the

fertilization envelope and highly

membrane it releases CGS P an enzyme

that Cleaves the proteins linking the of

ethylene envelope to the cell membrane

it also releases trans gluten - Proteus

in and many other proteins then we see

hydrogen peroxide is produced by the sea

urchin egg eventually forms ovo P it is

the udx one urgent dual oxidase which

drives the conversion of molecular

oxygen into hydrogen peroxide it's from

here Y from this hydrogen peroxide comes

now the T G + OE o P adds up together

and cross links the proteins and pour in

the fertilization envelope furthermore

ovo P or we can see over peroxidase also

interacts with Proteus a which

effectively settles over peroxidases to

the battalion layer furthermore we see

by the presence of h2o - generated by an

egg oxidase / peroxidase catalyzes the

formation of covalent tie tyrosine bonds

between proteins which again hardens the

fertilization envelope thus ensuring

that no additional sperm sneaks into the

egg so this is how the slow blocks to

polyspermy comes into play I hope you

liked the video if you liked it give it

a thumbs up do consider supporting my

work on patreon and also make sure to

subscribe this channel thanks